This invention relates to a pipette used for transferring a specified amount of liquid from one vessel into another vessel.
A pipette is generally used, for example, when a sample of liquid for test is transferred from a vessel for sample picking into a vessel for test. As a pipette of such kind, there is known one which has a small-diameter nozzle formed at the tip end of a body vessel and a suction chamber formed in a middle part of the body vessel.
The nozzle is put in a liquid in the vessel for sample picking with the suction chamber compressed, and the suction chamber is then reduced in pressure so that the pipette sucks a liquid sample. Thereafter, the nozzle is inserted into the vessel for test, and the suction chamber is then compressed again so that the pipette discharges the sucked liquid sample into the vessel for test, thereby transferring the liquid sample to the vessel for test.
The above-mentioned conventional pipette is a fixed-capacity type one that the amount of a single suction of liquid sample is fixed and therefore its range of use is limited, which invites poor versatility. For example, when urine is examined in a physical checkup or the like, picked urine is centrifuged, the supernatant fluid is then removed and 200 .mu.l of liquid is sampled. Thereafter, 200 .mu.l of liquid sample and the residue are mixed and from the mixture, 15 .mu.l of liquid sample for urine precipitation test is picked up. Thus, since the amount of suction of the conventional pipette is fixed, 200 .mu.l of sampling and 15 .mu.l of sampling cannot be readily switched, resulting in much expense in time and effort.
To cope with this, there is proposed a variable-capacity type pipette which is variable in sampling amount. However, although the pipette of this type has general versatility, it requires to set the sampling amount, which makes its operation inconvenient. In detail, in many cases, an operator executes sampling while holding the pipette with one hand. Therefore, when the pipette is held with one hand and the setting of the sampling amount is made with the other hand, both the hands are occupied, which makes prompt test execution difficult.
Further, since the variable-capacity type pipette has a complicated structure, this invites increase in number of parts and increase in cost.
The present invention has been made in view of the foregoing problems and therefore has its object of providing a pipette which is capable of selection between a large amount of sampling and a small amount of sampling and achieves a simple structure and a low cost.